1. Field of the Invention
The invention relates to a liquid cooling system for thermally highly stressed parts of industrial furnaces, with vertical cooling channels through which liquid flows.
2. Description of the Prior Art
Parts of industrial furnaces which are thermally highly stressed, eg. furnace walls, cover frames, door frames, gas removal nozzles etc. must be intensively cooled during operation in order to avoid deformation of these parts or even their destruction.
The parts to be cooled, particularly the walls of arc furnaces, have large surfaces. This means that the cooling liquid in the cooling systems must flow in such a way that as uniform as possible a cooling effect is achieved over the total furnace surfaces to be cooled. Perfect control of cooling in an industrial furnace by means of a liquid is of decisive importance for the operational safety of furnace operation, in order to protect the operating personnel from danger and to avoid material damage.
Such a liquid cooling arrangement is known from the publication "Wasserfuhrende Zustellung fur Elektrolichtbogen-Schmelzofen (Water-cooled Lining for Electric Arc Melting Furnaces)", undated, of Mannesmann Demag, particularly the illustration on the title page.
While there are with this vertical cooling system design advantages compared to the traditional horizontal helical arrangement of the cooling channels, too little attention is paid in this design to the problem of local overheating and gas bubble removal from the cooling system.
Gas bubbles can be formed in a cooling liquid in two different ways, either as steam, eg. with water cooling, or by separation of previously absorbed gases from the cooling liquid at elevated temperatures. The gases thus formed will collect in the upper tube bends and the flow velocity of the cooling liquid will be inadequate to transport the gases vertically downwards in order to move them through the lower tube bends into the next vertical tube section in the direction of the cooling liquid discharge. In the usual situation, the cooling channels will, according to the quantity of the gas, fill partially or completely with gas; the cooling liquid can then only pass through part of the cross-section of the cooling channels and in extreme cases will pulsate intermittently. In places where this happens, the cooling effect is considerably reduced and the whole cooling circulation comes to a stop. A further problem associated with the phenomena described above concerns the sizing of the cooling medium pump. This pump must produce an increased pressure when gas is present in the cooling circulation, which pressure corresponds to the sum of the heights of the pressure medium columns which are missing because of the gas content. An increase of the pump pressure over and above that required for the normal circulation of the cooling liquid would lead necessarily to the use of larger pumps and thus to higher investment costs.